Mandrels are essential tools in rolling and drawing steelmaking applications. As only one of many examples, mandrels can be used in cold drawing of tubular steel and other metal products. Cold drawing accomplishes the reduction of both the diameter and the wall thickness of a tube. Cold drawing of a tube through a fixed cold reduction die without an internal mandrel is called sinking, or sink drawing, in which only the diameter of the tube is reduced. When both wall thickness and tube diameter are to be reduced, it is more usual to place a mandrel within the tube prior to drawing the tube through a fixed cold reduction die.
Many steelmaking applications other than cold drawing, however, make use of mandrels for the shaping of steel and other metals. For example, mandrels are used for the hot rolling of steel pipe and, more specifically, are useful in a "cross rolling" mill where the mandrel rotates during processing. Mandrels are also used for "straight" rolling, and these mills are often referred to as mandrel mills.
Mandrels of this type are often of two-piece construction so that a dummy bar serves to give the assembly the required length and the attached work bar serves as the actual working part. After a certain period of use, the work bar must be replaced due to wear. The original welded assembly of most two-piece mandrels were traditionally quickly replaced by more convenient fastening arrangements such as by the use of screw threads or a simple pin. A number of prior art U.S. patents show work bars attached to dummy bars in this way, and these patents include U.S. Pat. No. 2,351,710 to Sanders, U.S. Pat. No. 3,901,063 to Nileshwar, U.S. Pat. No. 4,057,992 to Willimzik, U.S. Pat. No 4,161,112 to Stump and U.S. Pat. No. 4,745,787 to Sansome et al.
Unfortunately, prior art fasteners for two-piece, mechanically connected mandrels have never been adequately designed either to assure precise fitting or to provide the surface mating required to withstand and to transmit the forces incurred during normal mandrel operation. Torque-withstanding fasteners are particularly required in cross rolling applications when the mandrel must withstand rotation during use. A need thus remains for a precise fitting, force-withstanding connection between the dummy bar and the work bar segments of a mechanically connected mandrel assembly.